Support base



FIG. 1 is a perspective view of support base showing my new design.

FIG. 2 is a right elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a left elevational view thereof.

The rear view of the bathroom fixture support is not shown and is not part of the claimed design. 

I claim the ornamental design for a support base, as shown and described. 